Piezoelectric actuator and information storage apparatus

ABSTRACT

There are disclosed a piezoelectric actuator which can obtain large displacement at low voltage, which is small-sized and lightweight, and whose manufacture cost is low, and a small-sized lightweight information storage apparatus in which the piezoelectric actuator is incorporated, and which is provided with a small inertia moment during head driving and a high recording density. A piezoelectric actuator  200  includes a center body  200   a  and two spiral arms  200   b,  and two arms  200   b  are entirely in rotation symmetry and nonlinear symmetry.

BACKGROUND OF THE INVENTION

[0001] i. Field of the Invention

[0002] The present invention relates to a piezoelectric actuator, and aninformation storage apparatus in which the piezoelectric actuator isused.

[0003] ii. Description of Related Art

[0004] As an information storage apparatus built in or connected toelectronic apparatuses such as a personal computer and a word processor,a hard disk drive has been heretofore known. The hard disk drive isgenerally provided with a disk as an information storage medium, and ahead for reading/writing a recording bit with respect to the disk, andis also provided with an arm for holding the head in the vicinity of thedisk, and an electromagnetic actuator for driving the arm to move thehead along the disk.

[0005] A recording density of the hard disk drive has increased withdevelopment of the personal computer or the like, and particularly inrecent years, has rapidly increased with an increasing demand forhandling of image or music with the personal computer or the like.Moreover, with enhancement of the recording density of the hard diskdrive, recording bit on the disk has been finely divided, disk rotationspeed has increased, and high precision and high rate in positioning thehead have been requested. Furthermore, miniaturization, lightening andpower saving of the hard disk drive have also been promoted.

[0006] Therefore, in order to position the head at high precision andhigh rate, a hard disk drive has been proposed in which a piezoelectricactuator independent of the conventional electromagnetic actuator isdisposed midway on the arm.

[0007] However, the heretofore proposed piezoelectric actuator and harddisk drive have problems that sufficient displacement cannot beobtained, drive voltage is high, dimension and weight are large, inertiamoment during head driving is large, and manufacture cost is high.

[0008] These problems are not generated only in the hard disk drive, andare generally generated with respect to the information storageapparatus in which the head is held and moved by the arm.

SUMMARY OF THE INVENTION

[0009] The present invention has been developed in consideration of theaforementioned situations, and an object thereof is to provide apiezoelectric actuator in which large displacement is obtained at lowvoltage, which is small-sized and lightweight, and whose manufacturecost is low, and an information storage apparatus in which thepiezoelectric actuator is incorporated, whose inertia moment during headdriving is small, and which is high in recording density, small-sizedand lightweight.

[0010] In order to achieve the aforementioned object, according to thepresent invention, there is provided a first piezoelectric actuatorcomprising:

[0011] a piezoelectric layer which is formed of a piezoelectric materialof a two-dimensional shape provided with a central portion, and a groupof arm portions extended to the outside from the central portion inrotation symmetry and nonlinear symmetry, and which iscompressed/extended in an in-layer direction; and

[0012] a plurality of electrode layers for holding the piezoelectriclayer.

[0013] Here, the piezoelectric layer may be a flat layer having thetwo-dimensional shape, or a layer curved in the two-dimensional shape.

[0014] When a voltage is applied to the piezoelectric layer, thepiezoelectric layer is contracted in the in-layer direction. In thiscase, if tip ends of respective arm portions constituting the armportion group are fixed to a common rigid body, because of thetwo-dimensional shape, the central portion largely rotates at a lowvoltage. Moreover, since the structure of the first piezoelectricactuator of the present invention is easily manufactured, the firstpiezoelectric actuator can inexpensively be manufactured as asmall-sized lightweight actuator.

[0015] In the first piezoelectric actuator of the present invention, thearm portion constituting the arm portion group is preferably turned to abackside via the central portion with respect to a root by which the armportion is connected to the central portion.

[0016] Moreover, the first piezoelectric actuator of the presentinvention is preferably provided with a plurality of the piezoelectriclayers.

[0017] For the piezoelectric actuator including the arm portion turnedto the backside of the central portion, rotation amount of the centralportion is large for contraction amount of the arm portion. For thepiezoelectric actuator provided with a plurality of piezoelectriclayers, the contraction amount of the piezoelectric layer is large forthe voltage applied between the electrode layers. Therefore, by thesepiezoelectric actuators, larger displacement can be obtained at a lowervoltage.

[0018] When the first piezoelectric actuator of the present invention isprovided with a plurality of piezoelectric layers, the plurality of theelectrode layers of the same potential are preferably connected to oneanother by a via hole.

[0019] The piezoelectric actuator employing the via hole as means forconnecting the electrode layers to one another is easy in manufactureand low in manufacture cost.

[0020] Moreover, in the first piezoelectric actuator of the presentinvention, the piezoelectric layer is formed preferably of leadzirconate titanate (PZT) based piezoelectric ceramic, more preferably ofPNN-PT-PZ based piezoelectric ceramic.

[0021] As the piezoelectric material for forming the piezoelectriclayer, PZT, PT, barium titanate, layered perovskite and otherpiezoelectric materials can be utilized, but PZT based piezoelectricceramic is inexpensive, large in piezoelectric constant, and suitable asthe piezoelectric material for forming the piezoelectric layer.Particularly, a PNN-PT-PZ based piezoelectric material indicates aparticularly high piezoelectric constant among the PZT basedpiezoelectric materials, is superior in sinterability and is thereforeparticularly preferable as the piezoelectric material to form thepiezoelectric layer.

[0022] To achieve the aforementioned object, according to the presentinvention, there is provided a second piezoelectric actuator comprising:

[0023] a driving portion provided with a lamination structure includingat least one piezoelectric layer of a piezoelectric material and aplurality of electrode layers for holding the piezoelectric layer, andcompressed/extended in a lamination direction of the laminationstructure; and

[0024] a holding portion for holding a plurality of the driving portionsin an arrangement of rotation symmetry and nonlinear symmetry includingthe lamination direction in a predetermined common plane.

[0025] For the second piezoelectric actuator of the present invention,when the plurality of driving portions held by the holding portion areall compressed/extended, the aforementioned arrangement causes largerotation displacement at a low voltage. Moreover, since the structure ofthe second piezoelectric actuator of the present invention is easilymanufactured, the second piezoelectric actuator can inexpensively bemanufactured as the small-sized lightweight actuator.

[0026] The second piezoelectric actuator of the present invention istypically provided with two driving portions, and the typical secondpiezoelectric actuator is provided with an immobile portion adjacent tothe driving portion in a direction intersecting the direction in whichthe driving portion is compressed/extended,

[0027] Wherein the holding portion holds two pairs of the drivingportion and the immobile portion opposite to each other in such a mannerthat the driving portion of one pair turns the compressed/extendeddirection of the driving portion to the immobile portion of the otherpair.

[0028] Moreover, for the typical second piezoelectric actuator of thepresent invention, the holding portion preferably holds two pairs of thedriving portion and the immobile portion in such a manner that thedriving portion is disposed opposite to the immobile portion via a slit.

[0029] According to the piezoelectric actuator in which the drivingportion is disposed opposite to the immobile portion via the slit inthis manner, the driving portion is easily compressed/extended, andlarger displacement can be obtained at a lower voltage.

[0030] To achieve the aforementioned object, according to the presentinvention, there is provided a first information storage apparatuscomprising:

[0031] a head portion on which a head for performing at least one ofinformation recording and information reproduction with respect to apredetermined information storage medium is mounted;

[0032] an arm portion for holding the head portion in such a manner thatthe head mounted on the head portion is disposed in the vicinity of orin contact with the information storage medium;

[0033] an arm portion actuator for driving the arm portion to move thehead mounted on the head portion held by the arm portion along theinformation storage medium; and

[0034] a head portion actuator for rotating the head portion withrespect to the arm portion and centering on a gravity center of the headportion,

[0035] Wherein the head portion actuator comprises:

[0036] a piezoelectric layer which is formed of a piezoelectric materialof a two-dimensional shape provided with a central portion, and a groupof arm portions extended to the outside from the central portion inrotation symmetry and nonlinear symmetry, and which iscompressed/extended in an in-layer direction; and

[0037] a plurality of electrode layers for holding the piezoelectriclayer.

[0038] Here, the head may be a magnetic head or an optical head.

[0039] For the first information storage apparatus of the presentinvention, the head portion includes the head, and a slider, with thehead mounted thereon, for sliding on the information storage medium, thearm portion includes the arm driven by the arm portion actuator and asuspension connected to the arm, and the head portion actuator may bedisposed between the suspension and the slider.

[0040] Alternatively, for the first information storage apparatus of thepresent invention, the head portion includes the head, the slider, withthe head mounted thereon, for sliding on the information storage medium,and a suspension for holding the slider, and the head portion actuatormay be disposed between the suspension and the arm portion.

[0041] According to the first information storage apparatus of thepresent invention, since the head portion is rotated centering on thegravity center by the head portion actuator, the inertia moment duringhead driving is small, and head position can highly precisely becontrolled. Moreover, the head portion actuator is a small-sizedlightweight actuator similar to the first piezoelectric actuator.Therefore, the first information storage apparatus of the presentinvention is realized as a small-sized lightweight apparatus with a highrecording density.

[0042] Moreover, for the first information storage apparatus of thepresent invention, the head portion actuator is preferably joined to thearm portion by a portion corresponding to the tip end, of the armportion constituting the arm portion group, extending from the centralportion, and joined to the head portion by a portion corresponding tothe central portion. Furthermore, in the preferably constitutedinformation storage apparatus, the electrode layer is preferable in thatvoltage is applied to the head portion actuator in its portion connectedto the arm portion. The preferably constituted information storageapparatus is easily manufactured.

[0043] To achieve the aforementioned object, according to the presentinvention, there is provided a second information storage apparatuscomprising:

[0044] a head portion on which a head for performing at least one ofinformation recording and information reproduction with respect to apredetermined information storage medium is mounted;

[0045] an arm portion for holding the head portion in such a manner thatthe head mounted on the head portion is disposed in the vicinity of orin contact with the information storage medium;

[0046] an arm portion actuator for driving the arm portion to move thehead mounted on the head portion held by the arm portion along theinformation storage medium; and

[0047] a head portion actuator for rotating the head portion withrespect to the arm portion and centering on a gravity center of the headportion,

[0048] Wherein the head portion actuator comprises:

[0049] a driving portion provided with a lamination structure includingat least one piezoelectric layer of a piezoelectric material and aplurality of electrode layers for holding the piezoelectric layer, andcompressed/extended in a lamination direction of the laminationstructure; and

[0050] a holding portion for holding a plurality of the driving portionsin an arrangement of rotation symmetry and nonlinear symmetry includingthe lamination direction in a predetermined common plane.

[0051] Additionally, for the head portion actuator referred to in theinformation storage apparatus of the present invention, only a basicmode is described herein, but this simply avoids redundancy, and thehead portion actuator referred to in the information storage apparatusof the present invention includes not only the basic mode of the headportion actuator but also various modes of head portion actuatorsapplied to the aforementioned respective modes of the piezoelectricactuator.

[0052] Moreover, also for the second information storage apparatus ofthe present invention, to avoid redundant description, only the basicmode is described, but the second information storage apparatus of thepresent invention includes various modes of the second informationstorage apparatus applied to the respective modes of the firstinformation storage apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053]FIG. 1 is a diagram showing a first embodiment of an informationrecording apparatus according to the present invention.

[0054]FIG. 2 is an enlarged view in the vicinity of a suspension.

[0055]FIG. 3 is an enlarged view of a tip end portion of the suspension.

[0056]FIG. 4 is a diagram showing a shape of a piezoelectric layer.

[0057]FIG. 5 is a diagram showing the shape of a power supply electrodelayer.

[0058]FIG. 6 is a diagram showing the shape of a ground electrode layer.

[0059]FIG. 7 is a diagram showing wiring in the suspension.

[0060]FIG. 8 is a diagram showing a manufacture process of apiezoelectric actuator.

[0061]FIG. 9 is a diagram showing a second embodiment of thepiezoelectric actuator of the present invention.

[0062]FIG. 10 is an exploded perspective view in the vicinity of thesuspension in the second embodiment of the information storage apparatusof the present invention.

[0063]FIG. 11 is a diagram showing a third embodiment of thepiezoelectric actuator of the present invention.

[0064]FIG. 12 is a diagram showing the manufacture process of thepiezoelectric actuator of the third embodiment.

[0065]FIG. 13 is a diagram showing a fourth embodiment of thepiezoelectric actuator of the present invention.

[0066]FIG. 14 is a diagram showing a fifth embodiment of thepiezoelectric actuator of the present invention.

[0067]FIG. 15 is a diagram showing a process of forming a piezoelectricactuator lamination structure of the fourth embodiment.

[0068]FIG. 16 is a diagram showing the process of forming thepiezoelectric actuator lamination structure of the fifth embodiment.

[0069]FIG. 17 is a diagram showing a process of processing a calcinedmaterial into the piezoelectric actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] Embodiments of the present invention will be describedhereinafter.

[0071]FIG. 1 is a diagram showing a first embodiment of an informationrecording apparatus according to the present invention.

[0072] A hard disk drive (HDD) 100 shown in FIG. 1 shows the firstembodiment of the information recording apparatus of the presentinvention, and the first embodiment of a piezoelectric actuator of thepresent invention is incorporated. A housing 101 of the hard disk drive100 contains: a magnetic disk 103 attached to a rotation shaft 102 torotate; a slider 104 on which a magnetic head for performing informationrecording and information reproduction with respect to the magnetic disk103 is mounted; a suspension 108 for holding the slider 104 via thepiezoelectric actuator described later; a carriage arm 106 to which thesuspension 108 is fixed and which moves centering on an arm shaft 105and along the surface of the magnetic disk 103; and an arm actuator 107for driving the carriage arm 106. In the hard disk drive 100 shown inFIG. 1, the magnetic head and slider 104 constitute the head portionreferred to in the present invention, and the suspension 108 andcarriage arm 106 constitute the arm portion referred to in the presentinvention. Therefore, the arm actuator 107 corresponds to an arm portionactuator referred to in the present invention.

[0073] During recording of information into the magnetic disk andreproduction of the information stored in the magnetic disk 103, the armactuator 107 constituted by a magnetic circuit drives the carriage arm106, the piezoelectric actuator described later drives the slider 104,and the magnetic head is positioned in a desired track on the rotatingmagnetic disk 103. With rotation of the magnetic disk 103, the magnetichead mounted on the slider 104 successively approaches respective microareas arranged in respective tracks of the magnetic disk 103. Duringinformation recording, an electric recording signal is inputted to themagnetic head having approached the magnetic disk 103 in this manner,the magnetic head applies a magnetic field to the respective micro areasin response to the recording signal, and the information carried by therecording signal is recorded as a magnetization direction of therespective micro areas. Moreover, during information reproduction, themagnetic head extracts the information recorded as the magnetizationdirection of the respective micro areas as an electric reproductionsignal for the magnetic field in which magnetization is generated. Aninner space of the housing 101 is closed by a cover (not shown).

[0074]FIG. 2 is an enlarged view in the vicinity of the suspension 108shown in FIG. 1.

[0075]FIG. 2 shows the tip end portion of the carriage arm 106 shown inFIG. 1. As described above, the suspension 108 is fixed to the tip endportion of the carriage arm 106. The suspension 108 functions as a leafspring bent in a direction in which the magnetic disk is attached ordetached (vertical direction of FIG. 2). Moreover, the suspension 108holds the slider 104 via a piezoelectric actuator 200, and a magnetichead 109 is mounted on the slider 104. The piezoelectric actuator 200drives the slider 104 independently of the arm actuator shown in FIG. 1to slightly move the magnetic head 109. The piezoelectric actuator 200shows the first embodiment of the piezoelectric actuator of the presentinvention, and also shows one example of a head portion actuatorreferred to in the present invention. When the piezoelectric actuator200 slightly moves the magnetic head 109, the magnetic head 109 isexactly positioned.

[0076]FIG. 3 is an enlarged view of the tip end portion of thesuspension 108.

[0077] The piezoelectric actuator 200 is attached to an attachmentportion 108 a on the tip end of the suspension 108, and a periphery ofthe attachment portion 108 a is surrounded with a groove 108 c excludingan excessively narrow bridging portion 108 b. This particularly enhancesthe function of the suspension 108 as the leaf spring in the attachmentportion 108 a.

[0078] The piezoelectric actuator 200 includes a center body 200 a andtwo spiral arms 200 b, a tip end 200 c of the arm 200 b is fixed to theattachment portion 108 a, and the center body 200 a is fixed to agravity center of the slider 104. Moreover, the piezoelectric actuator200 is provided with a lamination structure including a piezoelectriclayer having a two-dimensional shape described later and an electrodelayer for holding the piezoelectric layer.

[0079]FIG. 4 is a diagram showing the shape of the piezoelectric layer,FIG. 5 is a diagram showing the shape of a power supply electrode layer,and FIG. 6 is a diagram showing the shape of a ground electrode layer.

[0080] A piezoelectric layer 201 shown in FIG. 4, a power supplyelectrode layer 202 shown in FIG. 5, and a ground electrode layer 203shown in FIG. 6 are laminated in order of the power supply electrodelayer 202, piezoelectric layer 201, ground electrode layer 203,piezoelectric layer 201, power supply electrode layer 202, piezoelectriclayer 201, . . . to constitute the piezoelectric actuator 200 shown inFIG. 3.

[0081] The piezoelectric layer 201 shown in FIG. 4 includes a centralportion 201 a, and two arm portions 201 b extending from the centralportion 201 a. These central portion 201 a and arm portion 201 bcorrespond to the center body 200 a and arm 200 b of the piezoelectricactuator 200 shown in FIG. 3, respectively.

[0082] Two arm portions 201 b constitute one example of an arm portiongroup referred to in the present invention, and the arm portion groupconstituted by two arm portions 201 b entirely indicates rotationsymmetry and nonlinear symmetry. Specifically, a symmetric axis existstwice in the central portion 201 a, two arm portions 201 b overlap witheach other by rotation movement of 180° centering on the central portion201 a, but no linear symmetry exists. Moreover, the respective armportions 201 b turn to a backside via the central portion 201 a withrespect to a root in which the arm portion 201 b is connected to thecentral portion 201 a. As described later, this structure causes largedisplacement at a low voltage.

[0083] Respective tip ends of two arm portions 201 b are provided withthrough holes 201 c through which via holes described later are passed.The present embodiment is provided with a plurality of piezoelectriclayers 201, so that drive voltage is lowered and displacement amount isincreased.

[0084] The power supply electrode layer 202 shown in FIG. 5, and theground electrode layer 203 shown in FIG. 6 are electrodes whose shapesare adapted for two arm portions 201 b shown in FIG. 4, and thepiezoelectric layer 201 is held between the power supply electrode layer202 and the ground electrode layer 203. When the drive voltage isapplied between the power supply electrode layer 202 and the groundelectrode layer 203, two arm portions 201 b are contracted. When thedrive voltage disappears, two arm portions 201 b are extended to returnto an original state.

[0085] A via 204 is connected to the power supply electrode layer 202 ina position of one of two through holes 201 c, and this via 204 connectsthe power supply electrode layers 202 to each other. Moreover, a via 205is connected to the ground electrode layer 203 in a position of theother through hole, and the via 205 connects the ground electrode layers203 to each other.

[0086]FIG. 7 is a diagram showing wiring in the suspension.

[0087] The suspension 108 is provided with a power supply wire 108 d andground wire 108 e connected to the attachment portion 108 a from theroot of the suspension 108 via the bridging portion 108 b, and the powersupply wire 108 d and ground wire 108 e are covered with an insulatingfilm. Moreover, respective tip ends of the power supply wire 108 d andground wire 108 e are provided with a power supply terminal 108 f andground terminal 108 g, and by a conductive adhesive layer 108 h formedon the power supply terminal 108 f and ground terminal 108 g, the tipend 200 c of the arm 200 b of the piezoelectric actuator 200 shown inFIG. 3 is fixed to the suspension 108. The power supply terminal 108 fand ground terminal 108 g are connected to the power supply electrodelayer 202 shown in FIG. 5 and the ground electrode layer 203 shown inFIG. 6 via the conductive adhesive layer 108 h, and this saves a wiringtrouble and lowers cost.

[0088] When the drive voltage is applied between the power supply wire108 d and the ground wire 108 e, the drive voltage is applied betweenthe power supply terminal 108 f and the ground wire 108 g, and betweenthe power supply electrode layer 202 and the ground electrode layer 203,and the arm portion 201 b of the piezoelectric layer 201 shown in FIG. 4is contracted in an in-layer direction. As a result, the arm 200 b shownin FIG. 3 is contracted.

[0089] Description will continue with reference to FIG. 3.

[0090] Since the tip end 200 c of the arm 200 b is fixed to theattachment portion 108 a as described above, on contraction of thepiezoelectric layer arm portion by the applied power supply voltage, aforce of attracting the respective arms 200 b of the piezoelectricactuator 200 toward the tip end 200 c is generated as shown by an arrowF1 of FIG. 3. Subsequently, by the force the piezoelectric actuator 200is deformed and the center body 200 a rotates in a direction of an arrowF2, and the slider 104 rotates in a direction of an arrow F3. As aresult, the magnetic head mounted on the slider 104 moves.

[0091] This action is generated even if the arm 200 b fails to besmoothly spiral as shown in FIG. 3, and the shape of the arm and armportion may be a shape constituted by joining rectangles, or anothershape, as long as a plurality of arms are formed entirely in rotationsymmetry and nonlinear symmetry. Therefore, a degree of freedom in theshape of the arm and arm portion is high.

[0092] Additionally, the force of attracting the respective arms 200 btoward the tip end 200 c as shown by the arrow F1 is a force of linearlyattracting the root connecting the arm 200 b to the center body 200 atoward the tip end 200 c, but similarly as the arm portion of thepiezoelectric layer, since the arm 200 b of the piezoelectric actuator200 turns to the backside of the center body 200 a, the root moveslargely around the center body 200 a. Therefore, even if the arm 200 bis slightly contracted, the center body 200 a rotates at a largerotation angle, and large displacement of a head position is thereforecaused at a low drive voltage. Additionally, when the arm 200 b furtherturns (e.g., around the center body 200 a once), the rotation angle ofthe center body 200 a further increases. Additionally, in this case,rigidity and workability of the piezoelectric actuator 200 aredeteriorated.

[0093] As described above, the center body 200 a of the piezoelectricactuator 200 is fixed to the gravity center of the slider 104. Moreover,the piezoelectric actuator 200 causes rotation displacement centering onthe center body 200 a, and the gravity center of the piezoelectricactuator 200 itself exists in the position of the center body 200 a.Therefore, when the piezoelectric actuator 200 is displaced to drive theslider 104 and magnetic head, the inertia moment is small, resonancefrequency of a composite material including the piezoelectric actuator200, slider 104 and magnetic head is high, and the composite materialcan make a high-rate response.

[0094]FIG. 8 is a diagram showing a manufacture process of thepiezoelectric actuator.

[0095] Here, the manufacture process is shown in which the piezoelectricactuator is manufactured by a green sheet lamination method utilized ina circuit substrate or the like.

[0096] First, a 65 μm thick green sheet 210 including PNN-PT-PZ basedpiezoelectric ceramic powder is molded by a doctor blade method in arange of a plurality of piezoelectric actuators (FIG. 8A).

[0097] Subsequently, via holes 211 each having a diameter of 50 μm arepunched in predetermined positions of the green sheet 210 (FIG. 8B).

[0098] Thereafter, by screen printing, an Ag-Pd electrode paste 212 isembedded in the via hole 211, and the Ag-Pd electrode paste 212 ispatterned/printed in an electrode layer shape shown in FIGS. 5 and 6(FIG. 8C).

[0099] The aforementioned respective processes are repeated a pluralityof times (four times herein) to form a laminate 213, and the laminate isunified by heating press (FIG. 8D).

[0100] Subsequently, the electrode paste is printed on a front surfaceand a back surface to form a surface electrode 214 (FIG. 8E), a spiralouter shape is formed by punching press and the respective piezoelectricactuators 200 are individualized (FIG. 8F).

[0101] Finally, degreasing and calcining are performed in the atmosphereto complete the piezoelectric actuator 200 (FIG. 8G). Processing may beperformed after calcining as occasion demands.

[0102] The piezoelectric actuator manufactured through the manufactureprocess is a piezoelectric ceramic solid, processing and assembly arehardly necessary, and manufacture can inexpensively be performed.

[0103] Moreover, the layers are easily and inexpensively connected toone another by the via holes, and can easily be connected to theterminal on the suspension by the surface electrode 214.

[0104] Additionally, here, after forming the laminate 213, the outershape of the piezoelectric actuator 200 is formed by punching press toindividualize the actuators, but the outer shape of the piezoelectricactuator 200 may be formed during punching of the via hole. Moreover,the piezoelectric actuator 200 may be individualized by ultrasonicprocessing, blast processing, laser processing, water jet processing,and the like, after calcining the laminate 213 shown in FIG. 8D,performing surface polishing and forming the surface electrode.

[0105] Moreover, the piezoelectric layer is formed by the green sheetmethod, but may be formed by a printing multi-layer method.

[0106] Furthermore, it is advantageous in respect of cost to integrallycalcine the surface electrode 214 as described above, but the laminate213 may be calcined before forming the surface electrode 214, and thesurface electrode 214 may then be formed by a printing method, gas phasemethod, or the like.

[0107] Here, the piezoelectric actuator 200 shown in FIG. 3 wasmanufactured by the manufacture process shown in FIG. 8 in the followingspecification.

[0108] Outer shape dimension: 1.0×1.0×0.16 mm

[0109] Weight: 0.8 mg

[0110] Drive layer (piezoelectric layer) number: 4 layers

[0111] Drive layer (piezoelectric layer) thickness: 40 μm

[0112] Piezoelectric material: PNN-PT-PZ based ceramic (piezoelectricconstant d31=300 pm/V)

[0113] Electrode material: Ag-Pd

[0114] When the piezoelectric actuator 200 of this specification wasfixed to the suspension 108 and slider 104 as shown in FIG. 3 andoperation characteristics were evaluated, movable distance of themagnetic head was 1.5 μm at a drive voltage of 12 V, positioningprecision of the magnetic head was 0.03 μm, and mechanical resonancefrequency was 12 kHz.

[0115] On the other hand, when no piezoelectric actuator was used andoperation characteristics only by the electromagnetic actuator wereevaluated for comparison with the present embodiment, the positioningprecision was 0.12 pm, and the mechanical resonance frequency was 600Hz.

[0116] Specifically, for the hard disk drive using the piezoelectricactuator of the first embodiment, the magnetic head can be moved at ahigh positioning precision and high rate, recording density can beincreased, and read/write rate can be increased.

[0117] The first embodiment of the information storage apparatus andpiezoelectric actuator has been described above, and a second embodimentof the information storage apparatus and piezoelectric actuator will bedescribed hereinafter. Additionally, different respects of the secondembodiment from the first embodiment will mainly be described, andredundant description is omitted.

[0118]FIG. 9 is a diagram showing the second embodiment of thepiezoelectric actuator of the present invention.

[0119] A piezoelectric actuator 300 of the second embodiment is similarto the piezoelectric actuator 200 of the first embodiment, except thatthe actuator is provided with a center body 300 a and four arms 300 b,and the piezoelectric actuator 300 of the second embodiment is alsoconstituted of the piezoelectric layer, power supply electrode layer,and ground electrode layer. Moreover, the piezoelectric layer is alsoprovided with the central portion corresponding to a center body 300 a,and four arm portions corresponding to four arms 300 b. When the drivevoltage is applied between the power supply electrode layer and theground electrode layer, according to a principle similar to that of thepiezoelectric actuator 200 of the first embodiment, the center body 300a rotates.

[0120]FIG. 10 is an exploded perspective view in the vicinity of thesuspension in the second embodiment of the information storage apparatusof the present invention.

[0121] The second embodiment of the information storage apparatus issimilar to the first embodiment of the information storage apparatusexcept that the piezoelectric actuator 300 is disposed between asuspension 110 and a carriage arm 111.

[0122] The center body 300 a of the piezoelectric actuator 300 is fixedto the gravity center of the head portion including a slider 112 withthe magnetic head (not shown) mounted thereon and the suspension 110,and tip ends of the respective arms 300 b of the piezoelectric actuator300 are fixed to respective fixing places 111 a on the carriage arm 111.Since displacement enlarging effect is exerted by a length of thesuspension 110, the displacement amount of the piezoelectric actuator300 may be smaller than that of the piezoelectric actuator 200 shown inFIG. 2.

[0123] The piezoelectric actuator 300 of the second embodiment wasmanufactured by the manufacture process shown in FIG. 8 in the followingspecification.

[0124] Outer shape dimension: 4.0×4.0×0.16 mm

[0125] Weight: 15 mg

[0126] Drive layer (piezoelectric layer) number: 4 layers

[0127] Drive layer (piezoelectric layer) thickness: 40 pm

[0128] Piezoelectric material: PNN-PT-PZ based ceramic (piezoelectricconstant d31=300 pm/V)

[0129] Electrode material: Ag-Pd

[0130] When the piezoelectric actuator 300 of this specification wasfixed to the carriage arm 111 and suspension 110 as shown in FIG. 10 andthe operation characteristics were evaluated, the movable distance ofthe magnetic head was 1.0 μm at a drive voltage of 12 V, the positioningprecision of the magnetic head was 0.07 μm, and the mechanical resonancefrequency was 8 kHz. Therefore, even for the hard disk in which thepiezoelectric actuator of the second embodiment is incorporated, themagnetic head can be moved with high positioning precision and at highrate, the recording density can be raised, and high-rate read/write canbe realized.

[0131] Additionally, in the aforementioned first and second embodiments,the center body of the piezoelectric actuator is fixed to a magnetichead side, the tip end of the piezoelectric actuator arm is fixed to anarm side, then the inertia moment can advantageously be reduced.However, in the mode of fixing the head actuator as referred to in thepresent invention, this mode is not limited, and for example, the centerbody of the piezoelectric actuator may be fixed to the arm side, whilethe tip end of the piezoelectric actuator arm may be fixed to themagnetic head side.

[0132] Moreover, in the first and second embodiments, the arm portion ofthe piezoelectric layer is disposed in symmetry twice and four times,but the arm portion referred to in the present invention may be disposedin symmetry three times or five times.

[0133] Furthermore, in the first and second embodiments, the number ofpiezoelectric layers is four, but the piezoelectric layer referred to inthe present invention may be of single layer or multiple layers. As thenumber of layers increases, low voltage, high displacement, and highrigidity are advantageously realized but the cost is increased.

[0134] Additionally, a conduction mode of the piezoelectric actuatorelectrode with the wiring on the suspension and arm is not limited tothe joining by the conductive adhesive, and conduction may be obtainedby soldering or by simple contact.

[0135] Moreover, as an inner layer electrode of the piezoelectricactuator, an Ag-Pd electrode, Pt electrode, and the like are suitable,because integral calcining with PZT based piezoelectric ceramic ispossible, but an Ag electrode, Ni electrode or the like can be utilizeddepending upon the piezoelectric material. On the other hand, theelectrode of the material using the same base as that of the inner layerelectrode is suitably used as the surface electrode. However, when thesurface electrode is formed after calcining, vapor deposition and othervarious electrode forming methods can be utilized, and a broad range ofmaterials can be utilized. The connection of the electrode layers is notlimited to the connection by the via hole, and connection along the sidesurface of the piezoelectric actuator may also be utilized.

[0136] Third, fourth and fifth embodiments of the piezoelectric actuatorof the present invention will next be described. The piezoelectricactuators of the third, fourth and fifth embodiments are incorporatedinto the information storage apparatus instead of the piezoelectricactuator incorporated into the information storage apparatus of thefirst embodiment. The information storage apparatuses provided with thepiezoelectric actuators of the third, fourth and fifth embodimentscorrespond to third, fourth and fifth embodiments of the informationstorage apparatus of the present invention. Only the third, fourth andfifth embodiments of the piezoelectric actuator will be describedhereinafter.

[0137]FIG. 11 is a diagram showing the third embodiment of thepiezoelectric actuator of the present invention.

[0138] A piezoelectric actuator 250 of the third embodiment shown inFIG. 11 is provided with a piezoelectric layer 251 including a centralportion 251 a and two arm portions 251 b, and a power supply electrodelayer 252 and ground electrode layer 253 between which a piezoelectriclayer 251 is held. For the piezoelectric actuator 250, the piezoelectriclayer 251 is curved in a two-dimensional shape referred to in thepresent invention. Therefore, the lamination direction of thepiezoelectric layer 251, power supply electrode layer 252, and groundelectrode layer 253 is different from the lamination direction in thepiezoelectric actuator of the first embodiment. However, when the powersupply voltage is applied between the power supply electrode layer 252and the ground electrode layer 253, similarly as the piezoelectricactuator of the first embodiment, the piezoelectric layer 251 iscontracted in the in-layer direction and the central portion 251 arotates.

[0139]FIG. 12 is a diagram showing the manufacture process of thepiezoelectric actuator of the third embodiment.

[0140] In the manufacture process, the piezoelectric material is firstextruded by a mouthpiece provided with an opening of the same shape asthe two-dimensional shape shown in FIG. 11, and a longitudinal material260 is formed whose sectional shape is a two-dimensional shape shown inFIG. 11 (FIG. 12A).

[0141] Subsequently, the power supply electrode layer 252 and groundelectrode layer 253 are formed on the peripheral surface of thelongitudinal material 260 (FIG. 12B). Finally, by slicing thelongitudinal material 260, the piezoelectric actuator 250 is obtained.

[0142] By the manufacture process, a large number of the piezoelectricactuators 250 are inexpensively manufactured.

[0143]FIG. 13 is a diagram showing a fourth embodiment of thepiezoelectric actuator of the present invention, and FIG. 14 is adiagram showing a fifth embodiment of the piezoelectric actuator of thepresent invention.

[0144] A piezoelectric actuator 400 shown in FIG. 13 is provided with alamination structure including a piezoelectric layer 401 of thepiezoelectric material, a power supply electrode layer 402, and a groundelectrode layer 403. The power supply electrode layers 402 or the groundelectrode layers 403 are connected to one another by external electrodesdisposed along the side surface of the piezoelectric actuator 400.

[0145] Moreover, the piezoelectric actuator 400 is provided with adriving portion 400 a of a layer structure in which the piezoelectriclayer 401 is held between the power supply electrode layer 402 and theground electrode layer 403, and an immobile portion 400 b in which thepiezoelectric layer 401 is held between the ground electrode layers 403.The driving portion 400 a is extended in the lamination direction(horizontal direction of FIG. 13) when the drive voltage is appliedbetween the power supply electrode layer 402 and the ground electrodelayer 403, and is compressed and returned when the applied voltagedisappears. Furthermore, other portions of the piezoelectric actuator400 excluding the driving portion 400 a and immobile portion 400 bfunction as a holding portion for holding the driving portion 400 a andimmobile portion 400 b, and this holding portion holds a integralstructure of the piezoelectric actuator by holding two driving portions400 a entirely in the arrangement of rotation symmetry and nonlinearsymmetry.

[0146] The piezoelectric actuator 400 is joined to the suspension by twoend joint materials 405, and joined to the slider by three middle jointmaterials 406. Moreover, when the driving portion 400 a is extended,three middle joint materials 406 rotate centering on the middle of thepiezoelectric actuator 400. Since the driving portion 400 a is providedwith a multilayered structure including a plurality of piezoelectriclayers, large displacement occurs at the low voltage.

[0147] Moreover, in the piezoelectric actuator 400, the driving portion400 a is disposed opposite to the immobile portion 400 b via a slit 404in the lamination direction of the lamination structure. Since the slit404 is disposed, a force generated by the extension of the drivingportion 400 a escapes and sufficiently large rotation displacementoccurs. The slit 404 extends to the inside from the side surface of thepiezoelectric actuator 400, and the integral structure of thepiezoelectric actuator 400 is held in the middle portion of thepiezoelectric actuator 400.

[0148] A piezoelectric actuator 500 shown in FIG. 14 is an actuatorequivalent to the piezoelectric actuator 400 shown in FIG. 13 exceptthat the structure of a slit 501 is different from the structure of theslit 404 shown in FIG. 13. Among elements constituting the piezoelectricactuator 500 shown in FIG. 14, the constituting elements equivalent tothe constituting elements of the piezoelectric actuator 400 shown inFIG. 13 are denoted with the same reference numerals as those shown inFIG. 13 and description thereof is omitted.

[0149] The slit 501 of the piezoelectric actuator 500 shown in FIG. 14exists in the middle portion of the piezoelectric actuator 500, and theintegral structure of the piezoelectric actuator 500 is kept in the sidesurface portion of the piezoelectric actuator 500. Since the integralstructure is kept in two places of the side surface portion, thepiezoelectric actuator 500 shown in FIG. 14 is higher in rigidity ascompared with the piezoelectric actuator 400 shown in FIG. 13.

[0150]FIG. 15 is a diagram showing a process of forming thepiezoelectric actuator lamination structure of the fourth embodiment,and FIG. 16 is a diagram showing the process of forming thepiezoelectric actuator lamination structure of the fifth embodiment.

[0151]FIG. 15 or 16 shows a process of once forming six laminationstructures of the piezoelectric actuator 400 shown in FIG. 13 or thepiezoelectric actuator 500 shown in FIG. 14, and each row divided by adashed line of FIG. 15 or 16 corresponds to one lamination structure.

[0152] Both in the forming processes shown in FIGS. 15 and 16, a greensheet 410 a using PNN-PT-PZ based ceramic powder is first formed, and aPt paste 411 of a first pattern corresponding to the ground electrodelayer 403 shown in FIGS. 13 and 14 is printed on the green sheet 410 a.The first pattern Pt paste 411 covers two lamination structures.

[0153] Subsequently, a green sheet 410 b is formed on the first patternPt paste 411, and a Pt paste 412 of a second pattern corresponding tothe power supply electrode layer 402 shown in FIGS. 13 and 14 is printedon the green sheet 410 b. The second pattern Pt paste 411 also coverstwo lamination structures, but a covering position is different fromthat of the first pattern Pt paste 411.

[0154] Thereafter, the formation of the green sheets 410 a, 410 b, andprinting of the first and second pattern Pt pastes 411, 412 are repeateda necessary number of times, and subsequently, a green sheet 410 c forcovering the printed Pt paste is formed.

[0155] Subsequently, in the forming process shown in FIG. 15, a paste413 mainly composed of a PVB binder is printed which has a third patterncorresponding to the slit 404 shown in FIG. 13. This third pattern isthe same as the second pattern corresponding to the power supplyelectrode layer 402, and the paste 413 mainly composed of the PVB binderdisappears during subsequent degreasing and calcining. After the thirdpattern paste 413 is printed, a green sheet 410 d for covering the thirdpattern paste 413 is formed. In the forming process shown in FIG. 15,the green sheet 410 d is in the middle of the lamination structure, andafter the green sheet 410 d, the aforementioned processes are repeatedin a reverse order. Therefore, a PVB binder paste 414 having a fourthpattern alternate with the third pattern is printed on the green sheet410 d to cover the third pattern paste 413.

[0156] On the other hand, in the forming process shown in FIG. 16, afterthe green sheet 410 c is formed, instead of the third pattern paste 413,green sheet 410 d, and fourth pattern paste 414, a PVB binder paste 415having a fifth pattern corresponding to the slit 501 shown in FIG. 14 isprinted.

[0157] Thereafter, both in the forming processes shown in FIGS. 15 and16, a green sheet 410 e is formed, and subsequently, printing of a Ptpaste 416 of a sixth pattern alternate with the second pattern andforming of a green sheet 410 f, and printing of a Pt paste 417 of aseventh pattern corresponding to the ground electrode layer and formingof a green sheet 410 g are repeated a necessary number of times.

[0158] By forming the laminate in this manner, degreasing the laminatein the atmosphere, and subsequently calcining the material, a calcinedmaterial provided with a desired lamination structure is obtained.

[0159]FIG. 17 is a diagram showing a process of processing the calcinedmaterial into the piezoelectric actuator.

[0160]FIG. 17A shows a calcined material 420 obtained by the formingprocess shown in FIGS. 15 and 16, and the lamination direction of thelamination structure of the calcined material 420 is a direction shownby an arrow F4. The calcined material 420 is cut into strip shapes inpositions corresponding to the dashed lines shown in FIGS. 15 and 16with a dicing saw or the like as shown by dotted lines. Thereby, asquare rod 421 is obtained as one lamination structure (FIG. 17B). In acut surface 421 a of the square rod 421, respective sections of thepower supply electrode layer and ground electrode layer are exposed in astate in which the power supply electrode layer and the ground electrodelayer are separated from each other. By forming an external electrode422 by vapor deposition or the like as shown in FIG. 17C, equipotentialelectrodes are connected to each other.

[0161] Thereafter, the square 421 is individualized/cut with the dicingsaw or the like as shown by dotted lines in FIG. 17D. Thereby, thepiezoelectric actuator 400, 500 is completed (FIG. 17E).

[0162] As described above, the piezoelectric actuators of the fourth andfifth embodiments can easily and inexpensively be manufactured by theprocesses shown in FIGS. 15 to 17.

[0163] Additionally, in the processes shown in FIGS. 15 to 17, the PVBbinder paste is used to form the slit, but another binder paste whichdisappears during degreasing or calcining may be used. Alternatively,after the calcined material is obtained, the slit may be formed by thedicing saw or the like.

[0164] Here, by the processes shown in FIGS. 15 to 17, the piezoelectricactuators of the fourth and fifth embodiments were formed with a drivingportion thickness of 20 μm and 20 driving layers (piezoelectric layers).Subsequently, when a drive voltage of 30 V was applied between the powersupply electrode layer and the ground electrode layer of the formedpiezoelectric actuator, and the displacement amount in the vicinity ofthe slit was measured, a large displacement amount of 250 nm or more wasindicated in either embodiment. Therefore, when the piezoelectricactuator is employed instead of the piezoelectric actuator of the firstembodiment, it is possible to position the magnetic head at a highprecision of several hundreds of nanometers.

[0165] Additionally, in the piezoelectric actuator of the presentinvention, the number of driving layers (piezoelectric layers) is notlimited to 20, and any number of layers may of course be formed.

[0166] As described above, according to the present invention, thelow-cost, high-performance piezoelectric actuator can be obtained.Moreover, when the piezoelectric actuator is incorporated, informationread/write precision in the information storage apparatus can largely beenhanced, and the small-sized lightweight information storage apparatuswith a high recording density can be obtained.

What is claimed is:
 1. A piezoelectric actuator comprising: apiezoelectric layer which is formed of a piezoelectric material of atwo-dimensional shape provided with a central portion, and a group ofarm portions extended to the outside from the central portion inrotation symmetry and nonlinear symmetry, and which iscompressed/extended in an in-layer direction; and a plurality ofelectrode layers for holding said piezoelectric layer.
 2. Apiezoelectric actuator comprising: a driving portion provided with alamination structure including at least one piezoelectric layer of apiezoelectric material and a plurality of electrode layers for holdingthe piezoelectric layer, and compressed/extended in a laminationdirection of the lamination structure; and a holding portion for holdinga plurality of said driving portions in an arrangement of rotationsymmetry and nonlinear symmetry including the lamination direction in apredetermined common plane.
 3. The piezoelectric actuator according toclaim 2 , comprising an immobile portion adjacent to said drivingportion in a direction intersecting the direction in which the drivingportion is compressed/extended, wherein said holding portion holds twopairs of said driving portion and said immobile portion opposite to eachother in such a manner that the driving portion of one pair turns thecompressed/extended direction of the driving portion to the immobileportion of the other pair.
 4. An information storage apparatuscomprising: a head portion on which a head for performing at least oneof information recording and information reproduction with respect to apredetermined information storage medium is mounted; an arm portion forholding the head portion in such a manner that the head mounted on saidhead portion is disposed in the vicinity of or in contact with saidinformation storage medium; an arm portion actuator for driving said armportion to move the head mounted on the head portion held by the armportion along said information storage medium; and a head portionactuator for rotating said head portion with respect to said arm portionand centering on a gravity center of the head portion, wherein said headportion actuator comprises: a piezoelectric layer which is formed of apiezoelectric material of a two-dimensional shape provided with acentral portion, and a group of arm portions extended to the outsidefrom the central portion in rotation symmetry and nonlinear symmetry,and which is compressed/extended in an in-layer direction; and aplurality of electrode layers for holding said piezoelectric layer. 5.An information storage apparatus comprising: a head portion on which ahead for performing at least one of information recording andinformation reproduction with respect to a predetermined informationstorage medium is mounted; an arm portion for holding the head portionin such a manner that the head mounted on said head portion is disposedin the vicinity of or in contact with said information storage medium;an arm portion actuator for driving said arm portion to move the headmounted on the head portion held by the arm portion along saidinformation storage medium; and a head portion actuator for rotatingsaid head portion with respect to said arm portion and centering on agravity center of the head portion, wherein said head portion actuatorcomprises: a driving portion provided with a lamination structureincluding at least one piezoelectric layer of a piezoelectric materialand a plurality of electrode layers for holding the piezoelectric layer,and compressed/extended in a lamination direction of the laminationstructure; and a holding portion for holding a plurality of said drivingportions in an arrangement of rotation symmetry and nonlinear symmetryincluding the lamination direction in a predetermined common plane.